Integrated circuits (IC's) typically include transistors and other circuit elements that are conductively interconnected in particular circuit configurations to provide desired circuit functions. Particular circuit elements and interconnection lines must be electrically isolated from other circuit elements and interconnection lines for proper IC operation. Modern IC technology includes insulating isolation layers. Such insulating isolation layers may be formed between transistors, between interconnection lines formed simultaneously, between interconnection lines formed as separate layers, between transistors and overlying interconnection lines, and as a passivation layer protecting underlying circuit elements and interconnection lines.
Good IC insulators should provide, among other things, low leakage currents, good mechanical strength, and low permittivity. In particular, a low permittivity insulator (also referred to as having a low relative or absolute dielectric constant) presents reduced parasitic capacitance between circuit nodes. Since parasitic capacitance between circuit nodes increases noise coupling and signal crosstalk between circuit nodes, increases power consumption, slows circuit operation, and potentially introduces timing faults, the parasitic capacitance associated with insulating IC isolation layers should be minimized.
Trends in modem semiconductor technology are increasing the importance of minimizing the parasitic capacitance of IC isolation layers. Consumers demand high speed operation of computer and memory IC's. Battery powered portable computer and communications devices demand low power consumption for prolonged operation between battery recharges. Portability also requires more dense circuits so that more functionality can be provided in a smaller product. As circuits become more dense, interconnection lines are more closely spaced, making signal crosstalk between circuit nodes a greater concern. IC isolation layers that minimize parasitic capacitance are essential to continued advancement in semiconductor technology.
One popular IC insulator, silicon dioxide (SiO.sub.2) has a relative dielectric constant (.epsilon..sub.r) of approximately 4.0. A smaller relative dielectric constant reduces the parasitic capacitance between circuit nodes. Ideally, the relative dielectric constant of an IC isolation layer should be reduced such that it approaches the relative dielectric constant of air (.epsilon..sub.r =1). Previous attempts to minimize parasitic capacitance have included forming air-gap dielectric structures having a relative dielectric constant approaching the relative dielectric constant of air (.epsilon..sub.r =1). Air-gap structures, however, tend to lack the mechanical strength needed to support overlying interconnection and isolation layers of high physical integrity. For the reasons stated above, and for other reasons that will become apparent upon reading the following detailed description of the invention, there is a need for providing a low dielectric constant IC insulator having better mechanical strength.